The present invention relates to endoscopy techniques and, in particular, it concerns a system and method for image-based alignment of an endoscope during at least part of an endoscopic procedure.
The present invention will be exemplified in the context of a system as described in the co-assigned PCT application published as WO 03/086498 entitled “Endoscope Structure and Techniques for Navigation in Branched Structure” to Gilboa, which is hereby incorporated by reference in its entirety. The aforementioned patent application discloses a method and apparatus in which a thin locatable guide, enveloped by a sheath, is used to navigate a bronchoscopic tool to a target location within the lung, aimed in particular to deliver treatments to the lung periphery beyond the bronchoscope's own reach. The coordinates of the target are predetermined based upon three-dimensional CT data. A location sensor is incorporated at the locatable guide's tip. The enveloped guide is inserted into the lung via the working channel of a bronchoscope. First, the bronchoscope's tip is directed to the furthest reachable location in the direction of the target. Next, the guide is advanced beyond the tip of the bronchoscope towards the designated target, based on the combination of the CT data and the position of the guide's tip as measured in body coordinates. When the guide's tip at the target, the guide is withdrawn, freeing the enveloping sheath for insertion a bronchoscopic tool. In order to prevent the distal end portion of the sheath from sliding away from the target, the sheath is locked to the bronchoscope's body and the bronchoscope itself is held steadily to prevent it from slipping further into the lungs or outwards. Because the airways in the periphery of the lung are narrow, approximately in the same dimensions as the sheath, sideways movements are extremely limited.
The above system may also be used to navigate the tip of the bronchoscope to a target located inside the main bronchus and not only to targets in the periphery of the lungs. Although for such centrally-located target the physician has direct visualization of the scene in front of the bronchoscope, it is not always sufficient for visually identifying the designated targets, since many of these targets are hidden in the tissue outside the airways. Hence, it is a benefit to combine the CT data into the navigational aids also for targets inside the main bronchus, where the bronchoscope can reach and direct vision exists, but yet the target itself is hidden.
When using the navigation system for navigating the tip of the bronchoscope itself, many of the mechanical features of the locatable guide described in WO 03/086498 are not needed. Specifically, the steerability of the guide is not needed, and the enveloping sheath is also not needed. However the principle of using a separate locatable guide having a location sensor at its tip and being inserted into the working channel of a regular bronchoscope actually changes the bronchoscope from a non-locatable bronchoscope to a locatable bronchoscope, thereby offering major advantages as will become clear.
As in the prior art apparatus, the locatable guide can be inserted into and withdrawn from the bronchoscope's working channel as needed. Unlike the periphery of the lung, the central airways are much wider than the bronchoscope. As a consequence, when the tip of the bronchoscope is on target, it can move sideways in addition to sliding in and out. Therefore stabilizing the bronchoscope's tip during treatment is a three dimensional task, involving the operation of the steering ability of the bronchoscope. An example for the importance for maintaining the location of the bronchoscope's tip at the designated target during the insertion of the bronchoscopic tool is the use of the Transbronchial Histology Needle, by which a needle is guided towards a target such as a lymph node which neighbors the main bronchus from the outside and thus is invisible to the bronchoscope image but its coordinates are known from the CT data. Any mistake in directing the needle may result not only in failure of the procedure, but worse, in causing damage to vital organs such as the aorta or other major blood vessels.
In principle, the same methods as presented in WO 03/086498 may be used in the context of the major airways. Specifically, by using the location of the tip of the bronchoscope as measured by the location measurement sensor, a directing display is produced corresponding to a simulation or schematic diagram of the view from the distal tip of the guide, which is based on the relative location of the target versus the position of the tip of the guide in six degrees of freedom. In the central airways, this view is supplemented by the direct video image from the bronchoscope imaging arrangement. Based on these two displays, the physician brings the tip of the bronchoscope to the target. When the tip of the bronchoscope is correctly aligned with and adjacent to the target (FIG. 7), the guide with the location sensor is withdrawn (as shown in FIG. 8), thereby freeing the bronchoscope's working channel for insertion a bronchoscopic tool FIG. 9a). Once the locatable guide is released, the directing display can no longer function for directing the tip to target. Instead, the physician has to hold the bronchoscope as steadily as possible during withdrawal of the guide and the insertion of the tool. If the bronchoscope slips from the target location (for example, as shown in FIG. 9b), the physician may notice the chance of position in the video image, but has no effective tool available to help him return the tip of the bronchoscope reliably to the desired target (other than reinserting the guide and repeating the navigation process).
Hence, it would be of benefit to have a method and corresponding system for confirming correct alignment of the tip of an endoscope after removal of a locatable guide used to achieve initial alignment, particularly for procedures involving a target which is obscured from view.